I have a plane that can fly on it's own following waypoints. What I would like to do is to have this plane flying around a big stockpile (or mine pit) by means of waypoints (there is a GPS on board), but have the onboard camera pointing the whole time to a predefined coordinated point at the center of this stockpile. The camera is controlled via servo motors.

Why are you expecting it to Serial2 can only communicate with Serial ports exposed as such by the OS or some other driver, like Bluetooth. As far as I know, and I have looked, there is no way to use a USB port under .NET on Windows Mobile without somebody writing a custom driver. Also the USB port on your Recon is, according to the data sheet, only a slave port so it won't be able to control USB devices even if you could get a driver written.

There may be a few others around but the only PDA I know of that has a Host USB port is the HP iPAQ214 (I have one, it has the normal slave port as well) but even then only drivers for USB mouse, keyboard and memory sticks are provided by the OS.